1. Field of the Invention
The invention relates to an LCD projection system, and more particularly, to an LCD projection system and illumination device thereof.
2. Description of the Related Art
Referring to FIG. 1, a typical illumination device 10 of LCD projection system comprises a light source 11, a first lens array 12, a second lens array 13, a PS converter 14, a condenser 15 and a relay 16. The illumination device 10 is used for converting the light beams from the light source 11 into p-polarized light or s-polarized light (depending on the design of the LCD projection system.) The polarized light is desired by the optical system of the LCD projection system, since only polarized light can cause the modulation of the liquid crystal particles when they enter the liquid crystal panel, and then have the effect of message transportation through the liquid crystal panel. For the convenience of designation and description, the p-polarized light is illustrated throughout the specification. The light source 11 comprises a lamp 111 and a parabolic lampshade 112. The lamp 111 is disposed at the focus of the parabolic surface of the lampshade 112 for providing parallel light beams to the first lens array 12.
The first lens array 12 and second lens array 13 are used for concentrating the light beams to the PS converter 14. Referring to FIGS. 2 and 3a, the PS converter 14 comprises a polarizing beam splitter set that is composed of a plurality of polarizing beam splitters 141, a plurality of metal blocks 142 and a plurality of half-wave retardations 143. The metal blocks 142 are disposed on the illuminated surface of the polarizing beam splitter 141. Each of the half-wave retardations 143 has the corresponding shape with the metal block 142, as shown in FIG. 3a, and is disposed on the output surface of the polarizing beam splitter 141. The output surface is opposite to the illuminated surface. Each of the half-wave retardations 143 has a birefringence polymer film. When a light beam passes through the film, the phase difference of the light beam on the ordinary axis of the polymer film differs with that on the extraordinary axis in a half period.
The light beam concentrated by the first lens array 12 and second lens array 13 must be designed to pass the clearance between the metal blocks 142, so that the light beam can pass through the polarizing beam splitter 141 without being blocked by the metal block 142. The light beam that passes through the polarizing beam splitter 141 can be split into p-polarized light (light 171) and s-polarized light (light 172), wherein the p-polarized light exits directly and the s-polarized light passes through the half-wave retardation 143 after reflection. Because the included angle between the slow axis of the half-wave retardation and the s-polarized light is 45 degrees, the s-polarized light can be converted into p-polarized light. Therefore, all the light beams can be converted into p-polarized light by the PS converter 14.
Referring to FIG. 3b, when it is desirable to convert the light beams into s-polarized light, the disposition of the half-wave retardation 243 must be different that of the half-wave retardation 143 in FIG. 3a. The light beam that passes through the polarizing beam splitter 241 can be split into p-polarized light (light 271) and s-polarized light (light 272), wherein the s-polarized light exits directly after reflection and the p-polarized light passes through the half-wave retardation 243 so that the p-polarized light can be converted into s-polarized light. Therefore, all of the light beams can be converted into s-polarized light by the PS converter 24.
However, since the metal blocks 142 block the light beams from passing through the polarizing beam splitter 141, the brightness efficiency is degraded. Further, the first lens array 12 and second lens array 13 must be designed to let the concentrated light beam pass the clearance between the metal blocks 142, so that the light beam can pass through the polarizing beam splitter 141. Therefore, the first lens array 12, second lens array 13 and PS converter 14 must be aligned and fit to each other, which will increase the difficulty of overall production and the cost, and reduce light efficiency.
Additionally, the polarization conversion efficiency (PCE) obtained by the typical illumination device 10 is usually 130 to 140%, hardly reaching the ideal value (160%), which is not good enough.
Consequently, there is a need for a novel and improved illumination device to solve above-mentioned problem.